1. Field of the Invention:
The present invention relates to a scanning probe microscope, and more particularly to an active cantilever equipped, scanning probe microscope with advanced functions combining the atomic force microscope (hereinafter abbreviated as AFM) and the scanning tunneling microscope (hereinafter abbreviated as STM) and to a method for measuring surfaces by using this novel microscope.
2. Prior Art
In early 1980s, STMs were developed as an apparatus allowing the observation of surfaces of solids with atomic-scale resolution. STMs utilize the phenomenon that a tunneling current flowing between an electrically conductive probe with a fine tip and the surface of a sample greatly depends on a distance between the probe and the surface of the sample. According to the STM measuring method, the probe scans the surface of the sample over its surface to observe the atomic arrangement while the tunneling current is maintained at a constant value. Furthermore, the measurement of electronic state density can be also executed by obtaining the voltage-current characteristics of the tunneling current.
Lately, some novel microscopes have been developed based on the principle of such a STM measurement.
Among them, AFMs are characterized by the detection of an attractive force or a repulsive force acting between the sample and the fine tip equipped probe, thereby enabling the measurement of roughness on the sample surface. In other words, the AFMs allow detailed observation, which was not achieved by the conventional STMs, on the surface structures of a wide range and a variety of materials, such as semiconductors, metals, organism and insulators.
However, these conventional STM and AFM, both a scanning probe microscope, have been encountered with the difficulty in identifying atomic species, in spite of the fact that they can assure the observation of atomic arrangement on the surface of metals, semiconductors, insulators, and the like. The AFM, if the probe is supported on a cantilever of a small spring constant to increase sensitivity in the vertical direction with respect to the sample, will encounter with another problem that, when the probe comes close to the sample, the cantilever is abruptly attracted toward the sample as soon as an attraction force acts between the sample and the probe. It means that the conventional AFM may not maintain the distance between the prove and the sample to cause a desired attracting force therebetween.